Command guidance transmitter system

ABSTRACT

A command guidance, ranging, and night vision system is provided which utilizes a single optical source. A gallium arsenide laser diode array generates pulses of optical energy in response to high frequency modulation by a transistor driver. The laser array is cryogenically cooled allowing diode array operation at high average power and enhancing the output wavelength. An image intensifier tube with a gating power source therefor is synchronized with the array output pulse, being gated on only when the reflected return signal is expected, sometime after the array output pulse is transmitted. The night vision intensifier tube is used in conjunction with the diode array by an operator to locate a target. When a target is located the gating capability of the night vision device is used to determine the range from the operator to the target.

iltute 1 States Patent 1 1 1111 3,751,166 Starkey et al. 1 Aug. '7, 1973[54] COMMAND GUIDANCE TRANSMITTER 3,463,588 8/I969 Meyerand, Jr. et aI356/5 SYSTEM 3,648,073 3 1972 Sams ct 111 .1 307/246 3,(1I4,()25 IO/l97lMaillct 244/316 I I Inventors: George y; Robert t 3.615.135 10 1971Frazer; 356/5 Jimmy R. Duke; Walter E. Miller, 3,644.043 2/1972 Jones etaI 356/5 Jr.. all of Huntsville, Ala. [73] Assignee: The United Statesof America as Z i g f f l f g i ti represented by the Secretary ol theArmy, Washington DC Azmrney-Harry M. Saragovitz et al.

[22] Filed". June 3, I97] 57 ABSTRACT [21] Appl. No.: 149,801 A commandguidance, ranging, and night vision system is provided which utilizes asingle optical source. A gal- [52] U S Cl 356/5 307/246 244/3 6 liumarsenide laser diode array generates pulses of opti- 1 cal energy inresponse to high frequency modulation by [51] um Cl GOlc 3/08 atransistor driver. The laser array is cryogenically [58] Mei! "55 4 5'cooled allowing diode array operation at high average 250/203 CT l6 3power and enhancing the output wavelength. An image 178mm 3O7/28 270intensifier tube with a gating power source therefor is synchronizedwith the array output pulse, being gated on only when the reflectedreturn signal is expected, [$6] References Cited sometime after thearray output pulse is transmitted. H The night vision intensifier tubeis used in conjunction UNHED S ATES PATENTS with the diode array by anoperator to locate a target. 3.305. 3 2/ Chcrmwh t I I 356/5 When atarget is located the gating capability of the g l l" night visiondevice is used to determine the range from yereta. U 3,397,404 8/1968Highleyman. 307/246 opumr to 3,380,358 4/1968 Neumann 356/5 1 Claim, 3Drawing Figures AR Y LASER BEAM OPTICAL DIODE FORMING OUTPUT DRIVERARRAY OPTICS SIGNAL T CRYOGENIC TRIGGER INPUT COOLER 12 FROM MISSILETRACKER RANGE DERIVATION |8 GATE a DISPLAY I TRIGGER VARIABLE GATEDDELAY NIGHT REFLECTION n----- MANUAL gag i? FROM TARGET DELAY ADJUSTPMENTEB 3.751.166

l4 Io I6 ARRAY LAsER BEAM OPTICAL DIoDE FORMING ouTPuT DRIVER ARRAYOPTICS sIGNAL I CRYOGENIC TRIGGER INPUT GooLER l2 FROM MIssILE TRACKER ERANGE DERIVATION l8 GATE a DISPLAY TRIGGER VARIABLE GATED DELAY NIGHTREFLECTION POWER VISION MANUAL SUPPLY DEVICE FROM TARGET DELAY ADJUST IGATE PULSE GATE DELAY (TUBE ON) x F TARGET AT V F l I I MAXIMUM I I L II BRIGHTNESS ""I 5*" REDUCED F P I F I BRIGHTNESS II I J L I I Is NOTEDT f 4 ROUND TRIP TIME I TIME GATE DELAY w 2 3 si LI 5 FIG. 3 I) (K t! 0w0. j 1 t S To LAsER ARRAY Robert L.Sitton JImmy R. Duke I4 WalterE.Mil|er Jr.

v INvEToRs.

COMMAND GUIDANCE TRANSMITTER SYSTEM BACKGROUND OF THE INVENTION Inexisting automatic command-to-line-of-sight missile systems a man isutilized for purposes of target location, identification, anddesignation. Target designation is accomplished by maintaining thecrosshairs of a telescope on the target during missile flight. Themissile is tracked automatically and correctional commands are generatedto maintain the missile flight trajectory coincident with the operator'svisual line-of-sight. In utilizing optical command guidance systems foradditional functions such as night illumination and ranging, additionalhardware such as gatable imaging devices are necessary. Whereas missilecommand functions require only a very narrowbeam pattern (less than 1),night illumination functions require a larger beam spread. An acceptableminimum night illumination and ranging beam intensity is a 3 vertical by5 horizontal beam. Uniform beam spread is required to permit theoperator to identify contrasting areas in the reflected image display astarget characteristics rather than be confused by holes or hot spots inthe beam. The center of the beam, used for missile communication, mustbe free of holes that can cause loss of command signals. Thus, beamforming optics must include an optical integrator which provides uniformradiance .of optical output energy, and can be imaged to provide theuniform intensity beam. This is done while maintaining the intensity andmodulation characteristics necessary for communicating commands to themissile.

SUMMARY OF THE INVENTION The command guidance transmitter systemprovides for the simultaneous functions'of night vision, target ranging,and commanding a missile. It is compatible with existing missile systemreceiver electronics and trackers. The system can be employed where onlythe functions of night vision and ranging are required, however it isnot limited only to night operation. With appropriate optical filteringit will provide adequate illumination for ranging and missile guidanceunder daytime conditions wherein the missile command function may beaccomplished even in the presence of solar interference. Only oneoptical source is required to provide the three functions of commandguidance, night vision, and ranging, affording advantages of savings inweight, volume, and system complexity. The optical energy output isderived from gallium arsenide (GaAs) laser diode arrays modulated at ahigh frequency rate to provide a pulsed output. By crygenically coolingthe laser arrays higher power outputs are obtainable from the system.

An object of the present invention is to provide a single system whichgives an operator the capability of performing the three functions ofnight vision, range determination, and optical command guidance signalfor missile delivery.

Another object of the present invention is to provide a gallium arsenidelaser diode array having a high frequency transistor driver andproviding high power optical energy output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram ofapreferred embodiment of the transmitter system.

FIG. 2 is a schematic diagram of a transistorized array driver.

FIG. 3 typically discloses ranging and range error determined by thesystem.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, a GaAslaser diode array 10 is positioned for cooling to cryogenic temperatures(approximately 77K.) by a cryogenic cooler 12. Array 10 is modulated bya driver circuit M to provide a pulse of laser energy which is formedand narrowed by beam forming optics l6 and directed toward a target ormissile. Array driver 14 is gated or triggered by an input signal frommissile tracking equipment to provide the high frequency periodicpulsing of diode array 10. An output signal from array driver 14 is alsocoupled through a variable delay power supply 17 to gated night visiondevice 18 for momentarily activating the device to receive reflectedenergy from the target or missile. The reflected optical energy receivedfrom a target is amplified by night vision device 18 for observing theimage of the target. The array driver output and the variable delaypower supply output are coupled to range derivation and displayelectronics 20, which converts the time difference in these two outputsinto range.

The gated night vision device isa three stage image intensifier tube,which is on only for the duration of the gate pulse received from powersupply 17. An image intensifier tube capable of providing the functionsrequired is model 3l68 manufactured by Varo Incorporated. The powersupply used with this image intensifier tube provides both gating anddelay functions and typically can be provided by model 23426manufactured by Venus Scientific Incorporated. These power sourcestypically can be gated at a lOK hertz rate with the gate pulse widthvariable from 0.5 to 1000 microseconds. The gate pulse can be externallytriggered for synchronizing the image intensifier tube on" time with anexternal event. The gating circuitry also provides a continuouslyvariable time delay between an external trigger pulse and the gate pulsewhich turns the tube The range derivation and display electronics 20 canbe any typical circuitry capable of measuring the elapsed time betweenthe occurrence of two pulses, converting this elapsed time to range byusing the velocity of light as a factor, and displaying the range forthe operator. Circuitry capable of performing this function can besimilar to that used in other range finder devices. Typically, anoscilloscope such as the Tecktronix model 585 can provide thiscapability.

A laser diode array 10 capable of providing sufficient illumination forthe transmitter system output is available from Laser Diode LaboratoriesIncorporated under part number LD440. The narrow spectral bandwidth ofthe optical output of laser diodes permits maximum filtering of anyunwanted background illumination. The fast rise time of the outputoptical pulse makes them ideal for the ranging functions. The laserdiode array is cooled to enhance the average output power capability andto shift the spectral output wavelength to a region in which the imageintensifier tube is more sensitive. Cooling of laser diodes alsosignificantly lowers their input current requirements thus makingpractical a completely transistorized array modulator.

Cryogenic cooler 12 allows the laser diode array to be operated at highaverage powers and enhances the output wavelength of the diode array. Italso lowers the input current requirements of the diode array. A coolercapable of performing this function is the Mark X60A manufactured by theMalaker Corporation. Since current requirements are quite small forcryogenically cooled laser diodes, the array pulsing and modulation isobtainable using completely transistorized circuitry for array driver14. A transistorized array driver 14 allows high pulse repetition ratesto be obtained from the laser diode array. Typical driver output is apulse train of one microsecond pulses at a nominal lOKhz repetionfrequency. The minimum pulse period is limited by the maximum gatingfrequency of the image intensifier. Driver output current is typically4.0 amperes peak at 400 volts.

In the array driver schematic of FIG. 2, transistors Q1, Q2 and Q3 arecascaded to provide a low voltage gate for a power transistor 04.TransistorQl has the collector connected through a resistor R1 to thecollector of Q3 and through a resistor R3 to the base of Q2. The emitterof O2 is connected through a resistor R4 to the collector of Q3 andfurther through resistor R10 to a direct current power source B+. Theemitter of O1 is connected through resistor R2 to ground and thecollector of O2 is connected through a poteniometer R5 to ground withthe variable arm of R5 being coupledto the base of 03, providing anexternal current adjustment for the driver. The emitter of O3 isconnected through the series connection of R6 and R7 to ground. A commonpoint between R6 and R7 is coupled to the base of power transistor 04which maintains 04 normally cut off. A capacitor C1 is strapped inparallel with resitor R6 allowing a positive voltage surge to be felt onthe base of 04 when transistor 03 activates. A high direct voltage inputB-l-lprovides dc power through a resistor R8 to the collector of 04, theemitter of 04 being connected through a resistor R9 to ground. A path toground is further provided from the collector of Q4through a couplingcapacitor C2 in series with a blocking diode D1 to ground. A commonpoint between C2 and D1 is coupled as an output signal to array 10 andvariable delay power supply 17. A positive trigger input pulse frommissile tracking equipment to the base of Q1 activates in sequence 01,Q2, Q3 and Q4. Prior to activation of Q4 capacitor C2 charges throughdiode D1. When Q4 is gated on, the B-H- side of C2 is immediatelydropped to near ground potential causing a high negative pulse to becoupled out for driving diode array 10.

For ranging, the image intensifier gate pulse width is set at lmicrosecond to match the optical pulse width, and the image intensifierdelay and gating circuitry is triggered by each optical pulse as itleaves the array. The delay capability of the night vision gatingcircuitry is used to locate the return pulse from the target. Thevariable delay of power supply 17 is manually adjustable by the operatorviewing the target through the image intensifier. The tube is thus gatedon at the instant each pulse is anticipated from the target. The imageintensifier tube integrates the train of pulses returning from thetarget thus making the target visible due to the total powerilluminating the target. By adjusting the delay between the time anoptical pulse leaves the laser array and the tube gate pulse, the targetbrightness can be varied. As noted in FIG. 3, ranging is accomplished byusing the delay time between the leading edge of the optical pulse, asit leaves the array and the leading edge of the gate pulse when a changein the brightness of the target is noted. This delay time is the roundtrip time of the optical pulse from the operator to the target and back.Since the velocity of light is constant the range from the operator tothe target is given by the equation: Range k (delay time)(velocity oflight). Alternately in determining range the gate pulse delay time maybe used at which the threshold of target detection occurs. This is thedelay time at which the irradience level on the target allows the targetto just become visible.

Attenuation of background optical noise is of particular importanceduring night time operation. Optical noise can cause scene degradationin the night vision device. Any optical source other than the includedtransmitter, in the field of view of the night vision device, isconsidered noise for this system. Typical noise sources are the missilemotor plume and on-board beacon used for tracking purposes. The imagetube is on only during the time optical returns are being expected fromthe target,'allowing attenuation of background noise. Furtherattenuation of background noise can be obtained by the use of a spectralbandpass filter in the night vision optical train. The operator can usethe night vision device 18 in conjunction with diode array 10 to locatea target without gating the device. However, when a target is locatedthe gating capability of the night vision device is used as hereinabovedescribed to determine the range from the operator to the target ifdesired. The night vision device allows track of the target while themissile is in flight and a coded input to the diode array allows themissile to be commanded while in flight, a coded input being derivedfrom the present missile system tracker output. Thus, in a missilecommand guidance system, a fixed tracking station is disposed fordistinguishing and maintaining track of a target. A command guidancetransmitter system includes a single optical source for providing nightvision, target ranging, target tracking, and command guidance of amissile. The laser array or optical source is driven by a high frequencymodulating means which is a high frequency transistor driving circuitfor pulsing the array on and off. When the diode array is periodicallyactivated at a high frequency rate to modulate the optical beam the beamis directed toward the target. Energy reflected back from the target isreceived and detected by the night vision means and range derivation anddisplay means respond to the night vision means to provide target range.

Although a particular embodiment and form of this invention has beenillustrated, it is obvious to those skilled in the art thatmodifications may be made without departing from the scope and spirit ofthe foregoing disclosure. Therefore, it is understood that the inventionis limited only by the claims appended hereto.

We claim:

l. A command guidance transmitter system including a single opticalsource for providing night vision. target ranging, and commanding amissile, comprising: a gallium arsenide laser diode array for providinga directional optical output, a high frequency transistor drivingcircuit for alternately pulsing said diode array on and off, saidtransistor driving circuit including a high means in the output path ofsaid array for compressing and expanding the beam spread of said array,increasing the operating range thereof, and range derivation and displaymeans responsive to said gated night vision means for providing saidtarget range.

1. A command guidance transmitter system including a single opticalsource for providing night vision, target ranging, and commanding amissile, comprising: a gallium arsenide laser diode array for providinga directional optical output, a high frequency transistor drivingcircuit for alternately pulsing said diode array on and off, saidtransistor driving circuit including a high power transistor outputstage having a common emitter and coupled to provide high frequencynegative output current pulses, and a low voltage, three stage cascadedtransistor gate for periodically activating said power transistor,cryogenic cooling means for said array, gated night vision means forreceiving and detecting reflected laser energy of said array, beamforming optical means in the output path of said array for compressingand expanding the beam spread of said array, increasing the operatingrange thereof, and range derivation and display means responsive to saidgated night vision means for providing said target range.